Battery enable and placement

i have a ninety four Hewes Bonefisher with a Yamaha ninety 2 stroke
I run the boat once or twice a thirty day period
Lights, bilge, Garmin D73v NO trolling motor. I want to incorporate a Bluetooth amp in the middle console to run some speakers at some level.
When I bought the boat in May well I was explained to the proprietor prior to my vendor experienced a trolling motor mounted off the stern on the poling system. The Boat has 1 battery with anything wired to it. There are some battery cables working from the middle console to the rear and…